Three new species of the genus Encentrum (Rotifera, Monogononta ...

Three new species of the genus Encentrum (Rotifera, Monogononta ...

Three new species of the genus Encentrum (Rotifera, Monogononta ...


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<strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>the</strong> <strong>genus</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>, <strong>Monogononta</strong>,Dicranophoridae)Willem H. De SmetSARSIADe Smet WH. 2000. <strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>the</strong> <strong>genus</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>, <strong>Monogononta</strong>,Dicranophoridae). Sarsia 85:77-86.<strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Rotifera</strong> belonging to <strong>the</strong> <strong>genus</strong> <strong>Encentrum</strong> (<strong>Monogononta</strong>, Dicranophoridae)are described and illustrated. <strong>Encentrum</strong> barti sp. nov. was found among algae in <strong>the</strong> Eastern Scheldtestuary, <strong>the</strong> Ne<strong>the</strong>rlands. Its main distinguishing taxonomic features are <strong>the</strong> rostrum provided with atriangular projection, <strong>the</strong> conical and slightly incurved toes, and <strong>the</strong> characteristic trophi. <strong>Encentrum</strong>listensoides sp. nov. was collected among algae in <strong>the</strong> Eastern Scheldt estuary, <strong>the</strong> Ne<strong>the</strong>rlands. Themain diagnostic features <strong>of</strong> this <strong>new</strong> <strong>species</strong> are <strong>the</strong> foot composed <strong>of</strong> three pseudosegments, a singlepair <strong>of</strong> large pedal glands, and <strong>the</strong> trophi showing asymmetrical unci, evenly curved manubria, andpreuncinal teeth set at a right angle to <strong>the</strong> axis. <strong>Encentrum</strong> tenuidigitatum sp. nov. was found inhygropsammon <strong>of</strong> a bight <strong>of</strong> <strong>the</strong> North Sea in Belgium. It is diagnosed by its slender, acutely pointedtoes, and <strong>the</strong> trophi bearing a tooth on <strong>the</strong> inner margin <strong>of</strong> <strong>the</strong> subbasal rami chambers.Willem H. De Smet, University <strong>of</strong> Antwerpen, R.U.C.A. campus, Department <strong>of</strong> Biology, Lab. PolarBiology and Palaeobiology, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.E-mail: wides@ruca.ua.ac.beKeywords: <strong>Rotifera</strong>; Dicranophoridae; <strong>Encentrum</strong> sp. nov.; Belgium; Ne<strong>the</strong>rlands.INTRODUCTIONDetailed studies on periphytic and psammic rotifers frommarine and brackish waters are very few on a worldwidescale. Most information is to be found in Remane1949; Pennak1951; Althaus 1957a, 1957b; Fenchel &Jansson 1966; Godske Eriksen 1968; Thane-Fenchel1968; Tzschaschel 1979, 1980, 1983; Turner 1990, 1993;and Saunders-Davies 1995. With <strong>the</strong> exception <strong>of</strong> <strong>the</strong>studies by Pennak (l.c.) and Turner (l.c.) which were donein North America, all o<strong>the</strong>rs concern European coastalwaters. The mentioned papers also account for most <strong>of</strong><strong>the</strong> rotifers known from periphytic and interstitial habitats<strong>of</strong> <strong>the</strong> littoral zone. The rotifer fauna <strong>of</strong> <strong>the</strong>se habitatsis considered impoverished relative to <strong>the</strong>ir freshwatercounterparts. This idea is probably correct; however,rotifer diversity is unquestionably underestimateddue to insufficient sampling efforts, preclusion because<strong>of</strong> <strong>the</strong> small size <strong>of</strong> <strong>the</strong> <strong>species</strong>, and difficulties in obtainingwell-preserved specimens. For <strong>the</strong> same reasonsit is likely that many unknown <strong>species</strong> await description.Dicranophoridae, and especially <strong>the</strong> <strong>genus</strong> <strong>Encentrum</strong>,are usually well represented in psammic-periphytic marineenvironments. The <strong>genus</strong> <strong>Encentrum</strong> is <strong>the</strong> most<strong>species</strong>-rich <strong>of</strong> <strong>the</strong> family Dicranophoridae. In a recentrevision, De Smet 1997 distinguished 90 <strong>species</strong>, <strong>of</strong>which 35 occur in brackish and marine habitats. Thepresent paper reports on three <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Encentrum</strong>discovered in Belgium and <strong>the</strong> Ne<strong>the</strong>rlands.MATERIAL AND METHODSThe <strong>species</strong> were sampled during an ongoing study on<strong>the</strong> rotifer fauna <strong>of</strong> <strong>the</strong> marine littoral habitats <strong>of</strong> <strong>the</strong>Belgian coast (North Sea) and <strong>the</strong> Eastern Scheldt estuary,<strong>the</strong> Ne<strong>the</strong>rlands.Plankton samples were collected by a horizontal haulwith a 40 µm plankton net. Hygropsammon was obtainedby scraping <strong>of</strong> <strong>the</strong> uppermost 0.5-1cm <strong>of</strong> <strong>the</strong> oxygenatedsand layer with a PVC bottle. Different <strong>species</strong> <strong>of</strong>seaweeds were sampled separately for <strong>the</strong> study <strong>of</strong>periphytic rotifers. Both samples for live examination,and samples fixed with formaldehyde to a final concentration<strong>of</strong> 4 %, were taken. The psammic and periphyticrotifers were extracted in <strong>the</strong> laboratory using <strong>the</strong> swirldecantationtechnique, and consequently concentratedon a 40 µm net.Animals were examined and drawn using a LeitzOrthoplan microscope with camera lucida. Preparation<strong>of</strong> trophi for light and scanning electron microscopy(SEM) was done following De Smet (1998) using NaOClsolution. For SEM a Philips SEM 515 microscope operatedat 20 kV was used.

78 Sarsia 85:77-86 – 2000TAXONOMIC REPORTFamily Dicranophoridae Harring, 1913Genus <strong>Encentrum</strong> Ehrenberg, 1838<strong>Encentrum</strong> barti sp. nov. (Figs 1, 2)Type locality. Eastern Scheldt, <strong>of</strong>f Oesterdam, <strong>the</strong> Ne<strong>the</strong>rlands.20 Feb 1996.Type material. Holotype: a female in a permanent glycerineglass slide mount deposited in <strong>the</strong> KoninklijkBelgisch Instituut voor Natuurwetenschappen (KBIN),Brussels, Belgium, No. IG 28.657. Paratypes: a male andtrophi preparation in KBIN; 5 slides containing femalesin <strong>the</strong> Department <strong>of</strong> Biology, RUCA, Antwerp, Belgium;1 slide with female and trophi in <strong>the</strong> Laboratory for AnimalEcology, RUG, Gent, Belgium.Material examined. 25 females and 6 males from typelocality.Distribution and ecology. Only known from type locality.It was collected among <strong>the</strong> red alga Callithamnioncorymbosum (Smith) Lyngbye from <strong>the</strong> infralittoral zone,and constituted <strong>the</strong> main rotifer component. Co-occurringrotifers were <strong>Encentrum</strong> algente Harring, E.listensoides sp. nov., E. marinum (Dujardin), Proaleshalophila (Remane), and P. reinhardti (Ehrenberg).Etymology. The <strong>species</strong> is named after my son Bart whocollected <strong>the</strong> red algae.Female. Body (Fig. 1A, B). Body fairly stout, fusiformin dorsal view, broadest near midlength. Head c. 1/3 totallength, <strong>of</strong>fset by neckfold, slightly tilted ventrally;dorsal antenna near neckfold. Rostrum short, decurvedventrally, broadly rounded with narrow triangular projectionmedially terminating in a papilliform structure.Corona oblique. Trunk without distinct folds, in lateralview dorsally arched and ventrally flattened; tail veryshort, broadly rounded; lateral antennae not seen. Footshort, conical, 2 pseudosegments. Toes (Fig. 1E, F) c. 1/7-1/8 total length, stout, tapering to acute points, basesslightly swollen, in dorsal view more or less conical,slightly incurved, in lateral view with curved dorsalmargin and almost straight ventral margin.Eyespots absent. Brain large, saccate, with Y-shapedduct; subcerebral glands present, with light-refractingglobule. Proventriculus present. Gastric glands large,rounded, apparently attached to proventriculus, no stalksseen. Two large pyriform pedal glands extending intotrunk and two small rounded pedal glands; reservoirslarge, in distal foot pseudosegment. Bladder normal.Vitellarium with 8 nuclei.Trophi <strong>of</strong> Isoencentrum-type (Figs 1G, 2A-F) accordingto De Smet (1997), relatively slender. Rami outlinemore or less heart-shaped; median rami opening broadlywedge-shaped; rami slender, each with slender, slightly<strong>of</strong>fset and incurved apical tooth, and stout preuncinaltooth set at a more or less right angle to axis; preuncinalteeth on a level with apical teeth. Fulcrum slightly lessramus length, narrow and parallel-sided in dorsal view,in lateral view with broad base and tapering posteriorly,slightly decurved ventrally. Unci single-too<strong>the</strong>d, fairlyslender, slightly curved; tooth shaft length, strongly expandedin <strong>the</strong> horizontal plane, broadest near mid-length;ventral and especially dorsal uncinal apophyses welldeveloped; foot <strong>of</strong> shafts distinctly broadened. Intramalleistrongly flattened, tapering to acute tip inwardly; outwardlyeach with two conspicuous spiniform processes.Supramanubrium inserted on anterior margin <strong>of</strong> intramallei,narrow with pointed ends, almost straight orslightly recurved anteriorly. Manubria more or lessstraight <strong>the</strong> greatest part <strong>of</strong> <strong>the</strong>ir length, slightly incurvedand crutched posteriorly, head slightly expanded withtriangular expansion and large opening.Measurements. Body length 93-130 µm, toe 14-17 µm.Trophi 25.5-27.3 µm : ramus 9.1-10.8 µm, fulcrum 7.5-9.1 µm, uncus 7.9-9.9 µm, intramalleus 1.2-2.2 × 4.7-5.1 µm, supramanubrium 5.6-6.3 µm, manubrium 19.5-20.9 µm.Male. Body (Fig. 1C, D) similar to that <strong>of</strong> female, butslender and on average smaller, with narrow neckpseudosegment. Trunk narrower posteriorly with shortproximal and long distal pseudosegment. Foot present,a single pseudosegment. Penis conspicuous.Measurements. Body length 95-115 µm, toe 10 µm.Remarks. <strong>Encentrum</strong> barti sp. nov. belongs to <strong>the</strong>sub<strong>genus</strong> Isoencentrum as defined by De Smet 1997, onbasis <strong>of</strong> <strong>the</strong> trophi morphology, especially <strong>the</strong> shape <strong>of</strong><strong>the</strong> rami outline, intramallei and fulcrum, and <strong>the</strong> presence<strong>of</strong> supramanubria.<strong>Encentrum</strong> barti sp. nov. is closely related to E. eristesHarring & Myers, 1928. It is distinguished from <strong>the</strong> latterby <strong>the</strong> presence <strong>of</strong> a triangular projection on <strong>the</strong> rostrum(absent in E. eristes), <strong>the</strong> in dorsal view more orless conical and slightly incurved toes (broadly bladeshapedand not incurved in E. eristes), <strong>the</strong> foot bearingtwo pseudosegments (a single pseudosegment in E.eristes), and its less oblique corona. Main differences introphi morphology concern <strong>the</strong> rami outline which isheart-shaped in E. barti and more elongate-pyriform inE. eristes, and <strong>the</strong> subbasal rami chambers being shorterand broader in E. barti.

De Smet – <strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>) 79Fig. 1. <strong>Encentrum</strong> barti sp. nov. A, Female, habitus, lateral view; B, Female, head and trunk, dorsal view; C, Male, habitus,lateral view; D, Male, habitus, dorsal view; E, Female, toes, lateral view; F, Same, dorsal view; G, Female, trophi, dorsal view.Scale bars A-D: 50 µm, E-G: 10 µm.<strong>Encentrum</strong> listensoides sp. nov. (Figs 3, 4)Type locality. Eastern Scheldt, tide puddle <strong>of</strong>f Zierikzee,<strong>the</strong> Ne<strong>the</strong>rlands. 22 Feb 1995.Type material. Holotype: a female in a permanent glassslide mount deposited in <strong>the</strong> Koninklijk Belgisch Instituutvoor Natuurwetenschappen (KBIN, Brussels, Belgium,No. IG 28.657). Paratypes: a trophi preparation in KBIN;several slides containing females and trophi in <strong>the</strong> Department<strong>of</strong> Biology, RUCA, Antwerp, Belgium; 1 slidewith female and trophi in <strong>the</strong> Laboratory for AnimalEcology, RUG, Gent, Belgium.Material examined. 50 females from type locality. EasternScheldt, <strong>of</strong>f Oesterdam, <strong>the</strong> Ne<strong>the</strong>rlands 3 specimens,20 Feb 1996.Distribution and ecology. So far only known from <strong>the</strong>Eastern Scheldt. It was found in a temporary tide puddle

80 Sarsia 85:77-86 – 2000Fig. 2. <strong>Encentrum</strong> barti sp. nov., female. A, Trophi (SEM), ventral view; B, Same, detail dorsal view; C, Same, detail ventralview; D, Same, dorsal, postero-lateral view; E, Same, ventro-apical view; F, Same, dorso-apical view. Scale bars: 10 µm.among <strong>the</strong> tube forming colonial diatoms Parlibellusdelognei (van Heurck) Cox and P. pseudocomoides(Hendey) Cox, and in <strong>the</strong> infralittoral <strong>of</strong> <strong>the</strong> EasternScheldt among <strong>the</strong> red alga Callithamnion corymbosum(Smith) Lyngbye. Accompanying rotifers: Colurellacolurus (Ehrenberg), <strong>Encentrum</strong> algente Harring, E. bartisp. nov., E. marinum (Dujardin), Proales halophila(Remane), P. reinhardti (Ehrenberg).Etymology. The Latin suffix -oides hints at <strong>the</strong> subtledifferences between this <strong>new</strong> <strong>species</strong> and E. listenseTzschaschel, 1978.Female. Body (Figs 3A, B) somewhat elongate-fusiform,broadest at c. 1/3 from anterior margin in dorsal view;cuticle sticky, covered with more or less dense layer <strong>of</strong>detritus. Head c. 1/5 total length, <strong>of</strong>fset by neckfold,

De Smet – <strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>) 81slightly tilted ventrally; 2 pseudosegments, anteriorsmallest, posterior with shallow dorso-lateral indentationon each side. Rostrum fairly small, broadly rounded.Corona strongly oblique. Trunk with 1-2 weak folds, inlateral view very slightly arched dorsally, highest in anteriorhalf, almost straight ventrally; tail broad; lateralantennae distally on trunk, slightly displaced dorsally.Foot short, 3 pseudosegments. Toes (Fig. 3C) c. 1/8-1/9total length, fairly slender, bases slightly swollen, graduallytapering to blunt tips, slightly decurved or kinkedventrally.Two colourless light-refracting globules near base <strong>of</strong>rostrum. Brain relatively small, saccate, subcerebralglands present, with light-refracting globule. Proventriculuspresent. Gastric glands ovate to kidney-shaped,stalked, with connection between brain and mastax; stalksanteriorly swollen, with light-refracting globules, especiallyin distal part. Two large spherical pedals glands,connected to toes by short tubule (Fig. 3C). Vitellariumwith 8 nuclei. Subitaneous egg ovate (Fig. 3E).Trophi <strong>of</strong> Isoencentrum-type (Figs 3D, 4A-E), robust,slightly asymmetrical. Rami outline more or less oval toroughly subhexagonal; median rami opening more or lessoboval; rami stout, slightly asymmetrical, each with apicaltooth, left apical tooth stronger and more incurvedthan right; prior to apical ramus teeth a single preuncinaltooth set at right angle to axis. Fulcrum ramus length,narrow and parallel-sided in dorsal view, in lateral viewwith broad base and tapering posteriorly, slightly decurvedventrally. Unci single-too<strong>the</strong>d, stout, slightlycurved, asymmetrical, right longer and <strong>of</strong> stronger build,tooth c. 3/5-3/4 shaft length, expanded in <strong>the</strong> dorso-ventralplane, broadest near base; ventral and especiallydorsal uncinal apophyses well developed; shaft withdorsal and ventral rib. Intramallei more or less trapezoid,broader than high, bearing elongate-triangular supramanubriumon anterior margin. Manubria equally curved,crutched posteriorly, head expanded with small triangularexpansion and large opening.Measurements. Body length 132-200 µm, toe 16-19 µm.Trophi 24.2-29.6 µm : rami 8.7-9.0 & 8.9-10.8 µm, fulcrum8.1-9.5 µm, unci 5.6-6.9 & 7.5-7.6 µm, intramalleus3.3-3.5 × 5.5 µm, supramanubrium 3.8-4.4 µm, manubrium17.4-20.9 µm. Subitaneous egg 36-39 × 60-64 µm.Male. Unknown.Remarks. <strong>Encentrum</strong> listensoides sp. nov. is to be placedin <strong>the</strong> sub<strong>genus</strong> Isoencentrum by <strong>the</strong> presence <strong>of</strong>supramanubria, <strong>the</strong> posteriorly tapering and ventrallydecurved fulcrum, and <strong>the</strong> shape <strong>of</strong> <strong>the</strong> rami outline.<strong>Encentrum</strong> listensoides sp. nov. shows a great similarityin overall body shape with E. listense Tzschaschel,1978. Both taxa are distinguished by <strong>the</strong> number <strong>of</strong> footpseudosegments (three in E. listensoides, one in E.listense), <strong>the</strong> number and shape <strong>of</strong> <strong>the</strong> pedal glands (asingle, large pair with short ducts in E. listensoides sp.nov. and two small pairs with conspicuous ducts in E.listense) and <strong>the</strong> shape <strong>of</strong> <strong>the</strong> toes (<strong>of</strong> more slender buildand tapering more rapidly in E. listensoides). In addition,length <strong>of</strong> body and toes is greater in E. listense.There are marked differences in <strong>the</strong> trophi morphologybetween both <strong>species</strong>. E. listensoides has distinctly asymmetricalunci (symmetrical in E. listense), and preuncinalteeth set at a right angle to <strong>the</strong> axis (parallel to <strong>the</strong> apicalrami teeth and oblique to <strong>the</strong> axis in E. listense). Themanubria <strong>of</strong> E. listense are straight and posteriorlyincurved, instead <strong>of</strong> being evenly curved as in E.listensoides.The <strong>new</strong> <strong>species</strong> cannot be confused with any o<strong>the</strong>rknown congener.<strong>Encentrum</strong> tenuidigitatum sp. nov. (Figs 5, 6).Type locality. Zwin Nature Reserve, located near Knokke,W. Flanders, Belgium, bight <strong>of</strong> North Sea. 14 Apr 1997.Type material. Holotype: a female in a permanent glycerineglass slide mount deposited in <strong>the</strong> KoninklijkBelgisch Instituut voor Natuurwetenschappen (KBIN),Brussels, Belgium. No. IG 28.657. Paratypes: one slidecontaining trophi preparation in KBIN; 5 slides containingfemales in <strong>the</strong> Department <strong>of</strong> Biology, RUCA, Antwerp,Belgium: 1 slide with female and trophi in <strong>the</strong>Laboratory for Animal Ecology, RUG, Gent, Belgium.Material examined. 17 females from type locality.Distribution and ecology. Only known from type locality.The <strong>new</strong> <strong>species</strong> was found in hygropsammon <strong>of</strong> <strong>the</strong>sandy beach, taken a few cm immediately above <strong>the</strong> wateredge. The accompanying rotifer fauna consisted <strong>of</strong> somebdelloid <strong>species</strong> and <strong>the</strong> monogononts Colurella colurus(Ehrenberg), <strong>Encentrum</strong> algente Harring, E. marinum(Dujardin), E. obesum Tzschaschel and Proalesreinhardti (Ehrenberg).Etymology. The <strong>new</strong> specific name tenuidigitatum (Latintenuis meaning thin, digitatum meaning provided withtoes) refers to <strong>the</strong> thin toes.Female. Body (Figs. 5A, B) fusiform in dorsal view,broadest somewhat before mid-length. Head c. 1/4-1/3total length, <strong>of</strong>fset by neckfold, 2-3 weak pseudosegments;tilted ventrally; dorsal antenna near neckfold.

82 Sarsia 85:77-86 – 2000Fig. 3. <strong>Encentrum</strong> listensoides sp. nov., female. A, Habitus, lateral view; B, Habitus, dorsal view; C, Toes, lateral view; D,Trophi, ventral view; E, Subitaneous egg. Scale bars A, B: 50 µm, C-E: 10 µm.Rostrum broad, rounded. Corona strongly oblique. Trunkwith inconspicuous folds, distally slightly wrinkled, inlateral view dorsally arched with weak hump in anteriorhalf, ventrally flattened; tail very short, broadly rounded;lateral antennae prominent, c. 2/3 <strong>of</strong> <strong>the</strong> way down body.Foot short, composed <strong>of</strong> one small pseudosegment bearingtoes, and two broader and wrinkled pseudosegments.Toes (Fig. 5C, D) c. 1/7 total length, slender, tapering toacute points, bases slightly swollen, in dorsal viewslightly incurved, in lateral view more or less stronglydecurved ventrally.A single colourless light-refracting globule at base <strong>of</strong> rostrum.Brain large, saccate, subcerebral glands present, withglobule. Proventriculus present. Gastric glands large, ovateto obovate, short-stalked, with connection between brain andmastax. Pedal glands large, ovate. Vitellarium with 8 nuclei.Trophi <strong>of</strong> <strong>Encentrum</strong>-type (Figs 5E, 6A-F), robust.Rami outline longer than wide; outer margin <strong>of</strong> ramislightly concave laterally, angular posteriorly; inner margin<strong>of</strong> subbasal chambers with angular tooth; rami terminatingin a slender, <strong>of</strong>fset and incurved apical toothset at almost right angle to <strong>the</strong> axis; prior to each apicaltooth ventrally a single, very stout preuncinal elementwith at right angle inwardly projecting triangular tooth;a small knob at middle <strong>of</strong> preuncinal tooth anteriorlywhereupon <strong>the</strong> ventral uncinal apophysis rests. Fulcrumlong c. 1.5 × ramus length, almost parallel-sided in dorsalview, in lateral view straight, broad at base, graduallynarrowing over c. 1/3 posteriorly and continuingparallel-sided. Unci single-too<strong>the</strong>d, slightly curved, toothc. 3/4 shaft length, more or less equally expanded allround, broadest near base; ventral uncinal apophysisweak, dorsal well developed. Intramallei trapezoid inlateral view, sock-shaped in ventral view, uncus lengthor slightly longer, opening large postero-laterally andinwardly. Manubria incus length, evenly curved, slightlytapering, crutched posteriorly, head with triangular expansiondorsally and ventrally; opening relatively small.

De Smet – <strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>) 83Fig. 4. <strong>Encentrum</strong> listensoides sp. nov., female. A, Trophi (SEM), ventral view; B, Same, detail dorsal view; C, Same, detailventral view; D, Same, detail dorso-apical view; E, Same, detail ventro-apical view. Scale bars: 10 µm.Measurements. Body length 80-127 µm; toe 13-19 µm.Trophi 23-24 µm : ramus 5.9-7.3 µm, fulcrum 8.6-9.3µm, uncus 5.0-7.1 µm, intramalleus 2.3-3.2 × 4 µm,manubrium 16.0-18.3 µm.Male. Unknown.Remarks. <strong>Encentrum</strong> tenuidigitatum sp. nov. should beplaced to <strong>the</strong> sub<strong>genus</strong> <strong>Encentrum</strong> De Smet, 1997 onbasis <strong>of</strong> <strong>the</strong> overall structure <strong>of</strong> <strong>the</strong> trophi, especially <strong>the</strong>rami outline, <strong>the</strong> shape and length <strong>of</strong> <strong>the</strong> intramallei, <strong>the</strong>absence <strong>of</strong> supramanubria, and <strong>the</strong> shape <strong>of</strong> <strong>the</strong> fulcrum.This <strong>new</strong> <strong>species</strong> can hardly be confused with any o<strong>the</strong>rcongener by <strong>the</strong> combination <strong>of</strong> its characteristic (1) slender,acutely pointed toes and (2) trophi bearing an angulartooth on <strong>the</strong> inner margin <strong>of</strong> <strong>the</strong> subbasal rami chambers.It superficially resembles E. eulitorale Tzschaschel,1978. However, <strong>the</strong> body <strong>of</strong> E. tenuidigitatum sp. nov. isfusiform and dorsally arched, whereas in E. eulitorale itis more or less parallel-sided and dorso-ventrally flattened.The toes <strong>of</strong> <strong>the</strong> <strong>new</strong> <strong>species</strong> are more slender andacutely tapering. E. tenuidigitatum also differs from E.eulitorale in trophi morphology. Its trophi are smaller(23-25 µm versus 40 µm in E. eulitorale), and <strong>the</strong> fulcrumis longer (1.5 × ramus length versus ramus lengthin E. eulitorale) and lacks <strong>the</strong> lateral and ventral expan-

84 Sarsia 85:77-86 – 2000Fig. 5. <strong>Encentrum</strong> tenuidigitatum sp. nov., female. A, Habitus, lateral view; B, Habitus, dorsal view; C, Toes, lateral view; D,Toes, dorsal view; E, Trophi, dorsal view. Scale bars A, B: 50 µm, C-E: 10 µm.sions at <strong>the</strong> posterior end as present in E. eulitorale. Themanubria are evenly curved and not incurved in threesteps as in E. eulitorale.The o<strong>the</strong>r <strong>species</strong> <strong>of</strong> <strong>the</strong> sub<strong>genus</strong> <strong>Encentrum</strong> displayinga triangular tooth on <strong>the</strong> inner margin <strong>of</strong> <strong>the</strong> rami are E.obesum Tzschaschel, 1979 and E. algente Harring, 1921.In E. obesum <strong>the</strong> body has its greatest width in <strong>the</strong> posteriorthird <strong>of</strong> <strong>the</strong> characteristic sack-shaped trunk (near mid-length<strong>of</strong> fusiform body in E. tenuidigitatum). Its toes are long (36µm), slightly decurved ventrally, with <strong>of</strong>fset and swollenbase (toes smaller (13-19 µm), more strongly decurved, andswollen bases not <strong>of</strong>fset in E. tenuidigitatum). The moreelongate intramallei and rami, with tooth on <strong>the</strong> inner marginsat 3/5 from <strong>the</strong> attachment to <strong>the</strong> fulcrum (near midlengthin E. tenuidigitatum), and <strong>the</strong> posteriorly incurvedmanubria <strong>of</strong> E. obesum (evenly curved in E. tenuidigitatum)unequivocally distinguish this <strong>species</strong> from E.tenuidigitatum.The <strong>new</strong> <strong>species</strong> is distinct from E. algente by itssmaller size and trophi length (80-127 µm versus 320-360 µm, and 23-24 µm versus 32-42 µm respectively),and especially <strong>the</strong> shape <strong>of</strong> <strong>the</strong> toes and trophi. Theslightly ventrally decurved toes <strong>of</strong> E. algente are basallyswollen and weakly <strong>of</strong>fset, reduced near mid-length andcontinuing more or less tubular to <strong>the</strong> acute tip. Maindifferences in trophi morphology are found in <strong>the</strong> moreelongate rami and intramallei, <strong>the</strong> shorter fulcrum, and<strong>the</strong> prominent tooth on <strong>the</strong> inner margin <strong>of</strong> <strong>the</strong> rami whichis lying at 3/5 from <strong>the</strong> base <strong>of</strong> <strong>the</strong> rami in E. algente.ACKNOWLEDGEMENTSI am indebted to <strong>the</strong> Department <strong>of</strong> Human Anatomy (Cell Biologyand Histology), University Centre <strong>of</strong> Antwerp for accessto <strong>the</strong> scanning electron microscope. Dr. L. Denys kindly identified<strong>the</strong> diatoms. This study was partially supported by a RAFOfund awarded by RUCA.

De Smet – <strong>Three</strong> <strong>new</strong> <strong>species</strong> <strong>of</strong> <strong>Encentrum</strong> (<strong>Rotifera</strong>) 85Fig. 6. <strong>Encentrum</strong> tenuidigitatum sp. nov., female. A, Trophi (SEM), dorsal view; B, Same, latero-ventral view; C, Same, detaildorsal view; D, Same, detail ventral view; E, Same, detail dorso-apical view; F, Same, detail ventro-apical view. Scale bars: 10 µm.

86 Sarsia 85:77-86 – 2000REFERENCESAlthaus B. 1957a. Faunistisch-ökologische Studien an Rotatoriensalzhaltiger Gewässer Mitteldeutschlands. WissenschaftlicheZeitschrift der Martin-Lu<strong>the</strong>r-UniversitätHalle-Wittenberg, ma<strong>the</strong>matisch-naturwissenschaftlicheReihe VI/1:117-158.Althaus B. 1957b. Neue Sandbodenrotatorien aus dem SchwarzenMeer. Wissenschaftliche Zeitschrift der Martin-Lu<strong>the</strong>r-Universität Halle-Wittenberg, ma<strong>the</strong>matischnaturwissenschaftlicheReihe VI/3:445-458.De Smet WH. 1997. The Dicranophoridae (<strong>Monogononta</strong>).Guides to <strong>the</strong> Identification <strong>of</strong> <strong>the</strong> Microinvertebrates <strong>of</strong><strong>the</strong> Continental Waters <strong>of</strong> <strong>the</strong> World. Volume 12, <strong>Rotifera</strong>5. SPB Academic Publishing, Amsterdam. p 1-325.De Smet WH. 1998. Preparation <strong>of</strong> rotifer trophi for light andscanning electron microscopy. Hydrobiologia 387/388(Developments in Hydrobiology 134):117-121.Fenchel T, Jannsson B-O. 1966. On <strong>the</strong> vertical distribution <strong>of</strong><strong>the</strong> micr<strong>of</strong>auna in sediments <strong>of</strong> a brackish water beach.Ophelia 3:161-177.Godske Eriksen B. 1968. Marine rotifers found in Norway, withdescriptions <strong>of</strong> two <strong>new</strong> and one little known <strong>species</strong>.Sarsia 33:23-34.Pennak RW. 1951. Comparative ecology <strong>of</strong> <strong>the</strong> interstitial fauna<strong>of</strong> fresh-water and marine beaches. L’Année Biologique27:449-480.Remane A. 1949. Die psammobionten Rotatorien der Nord- undOstsee. Kieler Meeresforschung 6:59-67.Saunders-Davies A. 1995. Factors affecting <strong>the</strong> distribution <strong>of</strong>benthic and littoral rotifers in a large marine lagoon, toge<strong>the</strong>rwith <strong>the</strong> description <strong>of</strong> a <strong>new</strong> <strong>species</strong>. Hydrobiologia313/314 (Developments in Hydrobiology109):69-74.Thane-Fenchel A. 1968. Distribution and ecology <strong>of</strong> non-planktonicbrackish-water rotifers from Scandinavian waters.Ophelia 5:273-297.Turner PN. 1990. Some interstitial <strong>Rotifera</strong> from a Florida,U.S.A., beach. Transactions <strong>of</strong> <strong>the</strong> American MicroscopicalSociety 109:417-421.Turner PN. 1993. Distribution <strong>of</strong> rotifers in a Floridian saltwaterbeach, with a note on rotifer dispersal. Hydrobiologia255/256 (Developments in Hydrobiology 83):435-439.Tzschaschel G. 1979. Marine Rotatoria aus dem Interstitial derNordseeinsel Sylt. Mikr<strong>of</strong>auna des Meeresbodens 71:1-64.Tzschaschel G. 1980. Verteilung, Abundanzdynamik und Biologiemariner interstitieller Rotatoria. Mikr<strong>of</strong>auna desMeeresbodens 81:1-56.Tzschaschel G. 1983. Seasonal abundance <strong>of</strong> psammon rotifers.Hydrobiologia 104:275-278.Accepted 19 May 1999 – Printed 24 March 2000Editorial responsibility: Jarl Giske

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